A client workstation on VLAN 30 (10.30.0.0/24) boots up and requires an IP address assignm… — CompTIA Network+

A client workstation on VLAN 30 ( $10.30.0.0/24$ ) boots up and requires an IP address assignment from a centralized DHCP server ( $192.168.100.10$ ) located across a routed core network. The local Layer 3 switch interface serving VLAN 30 ( $10.30.0.1$ ) is configured with a DHCP relay service (`ip helper-address 192.168.100.10`). Arrange the following steps in the correct chronological sequence representing the packet processing flow from the client's initial broadcast request through the relay agent's delivery of the DHCP Offer back to the host subnet.

1The host workstation broadcasts a `DHCPDISCOVER` packet with source IP $0.0.0.0:68$ and destination IP $255.255.255.255:67$ onto VLAN 30.
2The Layer 3 switch interface receives the broadcast, populates the `giaddr` field with $10.30.0.1$ , and unicasts the encapsulated packet with source IP $10.30.0.1:67$ and destination IP $192.168.100.10:67$ across the routed core.
3The central DHCP server evaluates the incoming `giaddr` payload ( $10.30.0.1$ ), selects an unassigned IP from the corresponding $10.30.0.0/24$ scope pool, and transmits a unicast `DHCPOFFER` payload directed to $10.30.0.1:67$ .
4The Layer 3 switch receives the unicast `DHCPOFFER`, inspects the `chaddr` client MAC address, and forwards the `DHCPOFFER` as a layer 2 broadcast or unicast frame targeted to port $68$ on VLAN 30.

Cevap

The correct chronological sequence is: 1) Host workstation broadcasts DHCPDISCOVER on VLAN 30. 2) Relay agent populates giaddr with 10.30.0.1 and unicasts request to server 192.168.100.10. 3) Server evaluates giaddr, allocates IP from 10.30.0.0/24 scope, and unicasts DHCPOFFER to 10.30.0.1. 4) Relay agent receives reply and delivers DHCPOFFER onto VLAN 30 to port 68.

The sequence follows the standardized DHCP relay mechanism. First, the unconfigured client broadcasts a DHCPDISCOVER on UDP port 67 within its local VLAN. Second, the Layer 3 switch acting as the relay agent intercepts the broadcast, inserts its ingress interface IP address (10.30.0.1) into the giaddr header field, and unicasts the packet to the central DHCP server IP address (192.168.100.10) on UDP port 67. Third, the central server uses the giaddr field to identify that the client resides on the 10.30.0.0/24 subnet, picks an available IP address from that pool, and responds with a unicast DHCPOFFER directed back to the relay agent's interface IP (10.30.0.1). Finally, the relay agent receives the offer, strips any relay-specific options, and transmits the DHCPOFFER to the host on VLAN 30 on UDP port 68.

Adım Adım Çözüm

Identify client initiation step

The host generates a local broadcast DHCPDISCOVER frame (0.0.0.0:68 -> 255.255.255.255:67) because it lacks an IP configuration.

DHCP clients start the DORA process by broadcasting to discover local or relayed DHCP services.

Analyze Relay Agent modification and forwarding

The L3 switch interface (10.30.0.1) receives the broadcast, inserts 10.30.0.1 into the giaddr header field, and converts the packet into a unicast frame sent to 192.168.100.10 on UDP port 67.

Routers drop limited broadcasts by default; relay agents bridge subnet boundaries by converting broadcasts to targeted unicasts with source subnetwork metadata (giaddr).

Determine server scope selection and response

The central server inspects giaddr (10.30.0.1), matches it to the 10.30.0.0/24 IP pool, and sends a unicast DHCPOFFER back to 10.30.0.1:67.

DHCP servers determine which address pool to lease from by examining the relay agent's giaddr field rather than the IP source header of the relay router.

Trace client-side delivery of the offer

The relay agent receives DHCPOFFER on UDP 67, references the client MAC (chaddr), and sends the DHCPOFFER onto VLAN 30 targeting UDP port 68.

The relay agent completes the return leg by delivering the server's offer back to the client's broadcast domain.

Anahtar Kavram

DHCP Relay Architecture and GIADDR Subnet Identification

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